Threadless connection of steel pipes

The formation of the pipeline involves the connection of pipes. for this, threaded and threadless methods are used. Which option is chosen depends on the purpose, location, material of the connected elements. But if threading is difficult, a threadless welded or fitting connection of steel pipes is used.

Threadless Connection Classification

Conditionally separate two methods:

• by welding. According to the conditions of the work, fusion welding and pressure welding are distinguished;
• using connecting fittings. In this capacity, couplings, flanges act.

Pros and cons of welding

This method gives a strong, airtight connection. Its advantages also include:

• there is no weighting of the system with additional details;
• process automation;
• for welding, there is no need to specially level the edge of the cut;
• suitable for systems of non-standard section elements: square. rectangular, oval. The connection of non-circular steel pipes on the thread is not possible.

Welding work is usually performed by a specialist and requires special equipment. Residual stresses arising at the joints can lead to depressurization of the joints under mechanical loads, vibrations. If repair is necessary, welded parts can only be cut off. It is technologically difficult to weld different metals (steel/cast iron), and it is impossible to weld different materials (steel/PVC). It is impossible to connect steel pipes with copper, aluminum by welding.

Pros and cons of a fitting connection

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The fitting connection provides a number of advantages without changing the requirements for joint tightness:

• all docking nodes are easy and quick to change;
• you can make changes to the system yourself by changing the type of fitting;
• if the pipeline breaks, fittings can be reused;
• no expensive special equipment is required;
• You can connect pipes from different materials.

Of the minuses, the impossibility of connecting slices with an angular section, the weighting of the system with additional elements are distinguished. Such a connection will serve for a long time with strict adherence to the installation technology.

Welding technology

Welding work is carried out using welding machines. In addition, transformers (rectifiers), a set of electrodes are used in electric welding. Be sure to work only in protective equipment.

For all types of welding, pipe sections are preliminarily prepared for welded seams: they are cleaned, the flange is cut, degreased, rust and paint are removed.

Further, the process depends on the welding method:

• The gas method involves the use of welding wire, with which the seam is filled in one go. In order to immediately get a high-quality result, you need to have special training. If, for technological reasons, the outer seam does not provide the necessary tightness, an internal seam is performed in front of it. Optimal for pipes with wall thickness up to 4 mm;
• The electric arc method requires centering, installation of pipeline elements in tacks. This is due to the fact that the work is done in parts. The seam is formed layer by layer. For each stage, an electrode of a larger diameter is taken. The method is applied to thick-walled pipes;
• Shielded welding is the most efficient way. The protection is a mixture of gases: argon, oxygen, carbon dioxide. The seam is neat and durable.

After welding in any way, the seam is cleaned of slag deposits, its tightness is checked. Welded joints are durable, aesthetic.

Couplings and their installation

In the threadless method, compression iron, metal-plastic, steel couplings, Gebo compression couplings are used.

Compression couplings have a sealing ring, a union nut. They do not provide complete reliability of fastening: with mechanical force, the pipe can be pulled out of the coupling. They are installed either as a temporary option at the repair stage, or where external influence is not expected.

Gebo compression couplings have three rings:

• clamping;
• sealing;
• clamping.

All elements are placed in a metal case, and with a clamping nut they form a common device. Such a coupling is effective when connecting steel structures with plastic, PVC pipelines. Scope of application: water supply, sewerage and gas systems where the pressure does not exceed 0.4 MPa. The positive aspects of using the Gebo coupling include:

• versatility of use;
• not subject to elastic deformations;
• the declared warranty period of use is more than 10 years;
• connection quality deviation of 3⁰ does not affect;
• no internal stresses;
• no metal fatigue.

Original Gebo couplings are sold with a passport.

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Mounting the compression sleeve

1. Cut two pipes.
2. Connect the slices and center them.
3. Make marks for the location of the coupling.
4. Lubricate the inside of the coupling and the outer pipe with sealants.
5. Put the coupling on the marked place and let it harden on the sealant.

Installation of the Gebo-coupling

1. A clamping nut is fixed on one of the parts of the pipeline.
2. Going to fitting starting.
3. The nut is tightened onto the parts, the rings are clamped inside.
4. Then everything is done for the second slice. The joint is sealed.

Flanges and their installation

The scope of the flange connection is fittings with a diameter of 50 mm. Flanges for pipes of smaller diameters are rare and are used only in exceptional cases.

Flange fitting design:

• metal ring with flanges located on both sides;
• sealing rings located inside the housing;
• fixing bolts.

The connection is reliable, easy to install, but the design has a significant weight and dimensions.

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Flange mounting

1. Determine the connection points and clean them of any plaque.
2. Put a flange on each connected element.
3. Installation of gaskets so that they extend beyond the edge of the pipe.
4. Bolt the flanges together. Internal seals will ensure the tightness of the joint.

In high-pressure pipelines, bolts are fixed by welding. If the fastener is tightened, care must be taken that it does not burst.

In order for docking to comply with regulatory requirements, it is necessary to consider:

• the type of gasket is selected depending on the purpose of the pipeline. for plumbing — porous cardboard impregnated with oil, for heating systems — asbestos cardboard;
• it is not advisable to install more than one gasket;
• gaskets must not come into contact with bolts. Their size is selected slightly larger than the diameter of the pipes;
• to evenly tighten the bolts, this is done in pairs, and not one after the other.

Installing a flange on a pipe is effective both for the method of threadless connection of steel pipes, and for eliminating leaks in emergency situations.

The use of fittings, couplings allows you to weld the pipe without threading and welding. But all connection methods are equal. Their choice depends on the specific installation conditions, pipe material, availability of tools.